1. Field of the Invention
This invention relates to pile driving hammers and in particular it concerns a novel diesel type pile driving hammer which is also capable of applying uplift blows as well as to a novel method for use of such hammer.
2. Description of the Prior Art
Diesel type pile driving hammers are well known in the construction industry. One example is the Model 520 Diesel Pile Hammer supplied by International Construction Equipment, Inc., 301 Warehouse Dr., Matthews, N.C. In a typical diesel hammer, a heavy ram falls in a cylinder onto an anvil mounted on the top of a pile. The impact of the ram on the anvil drives the pile down. During the fall of the ram, the air under the ram is compressed into one or more pockets formed in the upper surface of the anvil. At the time the ram strikes the anvil fuel is admitted to the pockets and mixes with the compressed air and explodes to drive the ram up for another stroke.
During the rise and subsequent fall of the ram, it passes by exhaust and inlet ports in the cylinder to allow discharge of the products of combustion and admission of fresh air to be compressed.
From time to time, in pile driving work, it becomes necessary to apply uplift blows to extract an object that has been driven. For example, some piles are installed by inserting a thick wall mandrel inside a thin walled tubular shell and driving on the mandrel to force the shell into the earth. The mandrel is thereafter extracted so that the shell, which remains in the ground, can be filled with concrete. During the driving operation the shell occasionally becomes squeezed against the mandrel, making the mandrel difficult to withdraw. When the mandrel has been hammered down with an air, steam or hydraulically driven hammer, the hammer is readily converted to uplift blow or "BUMPOUT" operation simply by reversing the controls or by turning the hammer upside down. Examples of such reversible hydraulic hammers are shown in U.S. Pat. Nos. 1,102,652, 1,292,429, 3,474,870, 3,583,499, 3,511,325 and U.S. Pat. No. Re. 28,151. There have also been disclosed reversible vibratory pile driving and extracting devices such as shown for example in U.S. Pat. No. 3,920,083. According to that patent the vibratory frequency is chosen to coincide with the resiliency and weight or force of the pile system during driving or extraction. There has also been proposed, in U.S. Pat. No. 4,159,039, a pile driving and extracting arrangement which makes use of the storage and selective release of strain energy in a deformable member to apply driving or extraction forces to the pile.
It has also been proposed to use diesel type hammers which are designed exclusively for generating uplift blows. Examples of such hammers are shown in U.S. Pat. No. 2,951,345 to A. Lang and in U.S. Pat. No. 3,109,500 to P. Glawon. The Lang hammer is actually a downward ramming hammer with a hydraulic motion reversing device. The Glawon hammer is a diesel hammer turned upside down. In both these diesel hammer arrangements there is produced a downward reaction which is substantially as great as the upward blow and which detracts from the ability of the hammer to extract the mandrel or other element to which it is connected. Also, neither the Lang or Glawon devices are designed to produce downward hammering blows.